Emphasis on renewable energy sources has been increasing due to concerns for reducing fossil fuel greenhouse gas emissions, reducing dependence on imported oil, providing a substitute for fossil fuels, and providing basic chemical constituents to be used in other industries, such as chemical monomers (e.g. xylene and ethylene glycol) for making plastics and the like. Biomass material, which is also referred to herein as lignocellulosic material, represents a vast amount of renewable resources available in virtually every part of the world and has the potential to satisfy at least some of the needs for sources of fuels and chemicals.
Lignocellulosic material is biomass that contains lignin, and cellulose or hemicellulose. Lignocellulosic materials include, but are not limited to, plant parts, fruits, vegetables, plant processing waste, wood chips, chaff, grain, grasses, corn, corn husks, and other agricultural residues, weeds, energy crops, aquatic plants, hay, paper, paper products, recycled paper and paper products, and any other lignin and cellulose or hemicellulose containing materials of biological origin. Lignin bonds to the cellulose or hemicellulose and has a molecular structure of a cross-linked phenolic polymer having an abundance of aromatic rings. Lignin is generally present in lignocellulosic material in an amount of about 15 to about 30 percent or more by weight. The aromatic hydrocarbon compounds that can be recovered from lignin (e.g., alkyl-benzene compounds and phenolic compounds) are valuable and can be used to produce various fuels and basic chemical constituents.
One conventional process for recovering aromatic hydrocarbon compounds from biomass is fast pyrolysis. In fast paralysis, the lignocellulosic material is heated to about 300 to about 900° C. in the absence of air forming solid products, liquid products, and gaseous pyrolysis products. A condensable portion (vapors) of the gaseous pyrolysis product is condensed into biomass-derived pyrolysis oil. Biomass-derived pyrolysis oil is a complex, highly oxygenated organic liquid having properties that currently limit its direct utilization as a biofuel or as a basic chemical constituent. Conversion of biomass-derived pyrolysis oil into an aromatic hydrocarbon-containing product that is useful as a biofuel and/or a basic chemical constituent requires additional operations to fully or partially deoxygenate the biomass-derived pyrolysis oil. These additional operations are expensive and time-consuming.
Another conventional process for recovering aromatic hydrocarbon compounds from biomass is by extracting and depolymerizing its lignin. As discussed in U.S. Pat. No. 5,959,167 and U.S. Patent Application Number 2010/0137663, lignin is depolymerized by exposing the lignin to a base catalyst having a pH of about 12.4 followed by hydrotreating to partially convert the lignin into aromatic hydrocarbon compounds. Unfortunately, this process requires large amounts of caustic materials for depolymerizing the lignin and therefore, is not environmentally friendly. Moreover, this process is relatively inefficient in that large amounts of the lignin are converted to coke rather than to aromatic hydrocarbon compounds.
Accordingly, it is desirable to provide methods and apparatuses for converting lignocellulosic material and/or lignin into an aromatic hydrocarbon-containing product without requiring expensive and time-consuming operations. Moreover, it is desirable to provide methods and apparatuses that are environmentally-friendly for converting lignocellulosic material and/or lignin into an aromatic hydrocarbon-containing product. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.